Various bearing assemblies for journaling the crankshaft within an internal combustion engine are known in the prior art. One of the most common types of such bearing assemblies generally includes a saddle member which is often integrally formed within the block of the engine, and a bearing cap which may be mounted over the saddle member. Both the saddle member and the bearing cap each include semi-cylindrical recesses of the same diameter, so that when the cap is bolted or otherwise mounted over the saddle member with the crankshaft captured therebetween, a cylindrical surface is formed which effectively journals the crankshaft in a running fit.
One of the primary advantages of such a bearing structure is that it allows the crankshaft to be removed from the engine block when it becomes necessary to replace the shaft, or perform other maintenance operations within the engine. Unfortunately, it has proven difficult to design a saddle and cap type bearing assembly which may be disassembled and reassembled repeatedly without some misalignment occurring between the abutting edges of the semicircular recesses in the saddle member and the bearing cap. The tolerances at the points of abuttment between the two semi-circular recesses are very narrow, and even small misalignments on the order of a few ten thousands of an inch can result in an engine which performs separately noisier and rougher. Worst still, such misalignments often accelerate the wear of the crankshaft, and reduce the reliability of the engine as a whole. Such unreliability is particularly unacceptable in the diesel engines used in the trucking industry, where unexpected engine down-times may be very costly.
The prior art has a tendency to solve this misalignment problem in several ways. For example, in some bearing assemblies, vertical location surfaces are provided along the edges of the bearing cap which are engageable with guide surfaces present on either side of the semi-cylindrical alignment slot of the saddle member. When the locating surface to the bearing cap are captured within the guide surfaces of the alignment slots, the bearing cap is prohibited from moving transversely relative to the saddle member. Still another solution has been the provision of stepped contacting faces on either end of the bearing cap which are mateable within stepped alignment slots in the saddle member. In a variation of this same concept, serrated mating faces or meshing teeth may also be provided on either end of the bearing cap in order to align the easily abutting edges of the semi-cylindrical alignment slots of the bearing cap and the saddle member and to prohibit transverse movement between the cap and the saddle member. In most such arrangements, pilot bolts are inserted into either end of the bearing cap and screwed into registering bores in or near the alignment slots of the saddle member in order to secure a mount at the ends of the bearing cap securely within the alignment slots of the saddle member.
Unfortunately, such prior art solutions to the misalignment problem are not without shortcomings. For example, the generally symmetrical shape of prior art bearing caps renders it very easy for a mechanic who disassembles such a bearing assembly to erroneously reassemble the bearing cap back over its respective saddle member with the ends of the bearing cap 180.degree. reversed. If the axis of rotation of the semi-cylindrical alignment slot of the bearing cap is perfectly machined the same distance with respect to the vertical location surfaces on either end of the cap, then such a 180.degree. reversable may be of no consequence. However, in more cases than not, such a mis-assembly of the bearing will result in wear-increasing misalignments. Still another shortcoming associated with prior art solutions is the number of precision guide surfaces and pilot holes which need to be machined to the ends of the bearing cap and saddle member in order to achieve the desired, precise alignment between the abutting edges of the semi-cylindrical recesses of the cap and saddle member.
Clearly, there is a need for a bearing assembly which may be disassembled, and unambiguously reassembled in order to maintain the precision alignment between the semi-cylindrical recesses of the cap and saddle member. Moreover, it would be desirable if such a structure required a minimal number of guide surfaces and pilot bores in order that it may achieve its function with a maximum of reliability, and a minimum of costly machining.